1. Field of the Invention
This invention relates to coordinate measuring instruments, and more particularly to improvements in a touch signal probe used in this coordinate measuring instrument, for sensing a contact with a workpiece to be measured.
2. Description of the Prior Art
In general, the touch signal probe utilized in the coordinate measuring instrument is classified into two types including a contact type for electrically detecting a mechanical displacement when a contact element comes into contact with the workpiece and a conduction type for detecting an electrical conduction with the workpiece. Each of the touch signal probes is of such an arrangement that a sensor having the contact element thereon is held on a main body of probe through an origin returning mechanism in a manner to be swingable and restorable to a predetermined posture.
Now, with the conventional touch signal probe, in order to change a direction of the contact element contacting the workpiece, such a change in posture should be made so that the probe itself is replaced by another one or the probe is inclined to a main body of the measuring instrument.
However, in changing the direction of contact through the above-described methods, the posture cannot be easily changed, due to the accuracy of coupling of a probe shank to the main body of the measuring instrument, and the contacting portion of the contact element being varied in the positional relationship with the main body of the measuring instrument. As the result, each time the direction of contact of the contact element is changed, a so-called origin check works or procedure should be made to specify a system of coordinates in the direction of contact thus changed. This complicates the working, and further, makes it necessary to provide a device for changing to absolute coordinates, thus rendering it uneconomical. Particularly, in the case of measuring the continuous curved surfaces such as a mold for molding eyeglass frames and the like, the frequency of changes of the contacting directions is high, thereby presenting such a disadvantage that the measured data become rough.
In fact, if the contact element is formed into a ball shape, then the omnidirectional characteristics may be obtained. However, it becomes necessary to provide a device for correcting a diameter of the ball. In particular, it is difficult to install the main body of the measuring instrument and the probe concentrically with each other, whereby the origin check works should be carried out each time the posture is changed, thus not enabling to settle the matter radically.